1. Field of the Invention
This invention relates to microcoils and their construction. Specifically, this invention relates to microcoils for use in medical devices used to obtain a magnetic resonance image of a region within a natural organism or patient (such as within a human) or elsewhere.
2. Background of the Invention
The use of magnetic resonance medical devices provides enhanced imaging within the region of interest and can be used for various internal procedures including targeted drug delivery. The term microcoil or MR microcoil is used to denote a magnetic resonance device used for imaging internally from a patient. This term is in contrast to MR coils that are conventionally used externally to the body for MR imaging purposes. A microcoil may contain one winding of electrical conductor, or multiple windings that are spaced a distance apart from each other. Typically multiple windings are joined together at a predetermined spacing with the planes of the windings parallel to each other.
The MR microcoil may be mounted at the tip of a catheter or other insertion device used to probe the interior of a body. The combination of the microcoil mounted on another device provides quick and direct access to the region where imaging is required. Medical procedures such as image-guided and minimal access surgery, performed within small regions of a patient's anatomy, demand the ability to visualize the internal terrain and/or the procedure being performed by the surgeon. While alternative methods, including x-ray imaging and fiber optic viewing offer possible alternative means of performing the visualization of terrain and the location of physical secondary devices, magnetic resonance imaging methods are a particularly convenient means of doing this, especially given the highly localized nature of the procedures being performed.
As with any manufactured device, new methods of manufacturing components are always being pursued to enhance performance and lower manufacturing costs. Conventionally, microcoils are manufactured by hand winding of an electrical conductor around a mandrel, or alternatively machine winding an electrical conductor around a mandrel. The resulting winding may have to be removed from the mandrel, and the leads for each end of the winding must be isolated. Additionally, where multiple windings are joined together in a device, the ends from multiple windings need to be connected. Handling windings in the manufacturing process can cause damage to the fragile windings resulting in manufacturing yield loss. The trend of smaller devices only increases this problem. With minimally invasive surgical procedures, the electrical conductor diameters used must be increasingly smaller to provide smaller coils. These coils are more easily damaged.
In manufacturing microcoils, there are also dimensional control variations within a single winding, and between windings. The diameter of the an electrical conductor used in a single winding may vary and affect the electrical characteristics of the resulting winding. Similarly, the insulating coating around the electrical conductor may vary in thickness and affect the electrical properties of the winding.
From one winding to another, variations in electrical conductor diameter and coating thickness are still a manufacturing variable. In addition, the number of turns from one winding to the next must be controlled by measuring the length of electrical conductor used in each winding. Also, the distance between windings in a microcoil containing multiple windings must be controlled by carefully joining the ends of a conventional winding at a measured distance.
While these conventional approaches to the manufacture of windings and microcoils result in functioning microcoils, the process is time consuming with several steps. Manufacturing yield is a problem due to the handling necessary in the conventional process, and consistent quality control is difficult.